


A Heated Exchange

by PurrfecktlySinful



Category: Undertale (Video Game)
Genre: Arguing, Ecto-Genitalia (Undertale), Ecto-Penis (Undertale), Ecto-Tongue (Undertale), Ecto-Vagina (Undertale), Fingering, Fluff, M/M, Painful Sex, Rough Sex, but Sans likes it, heat - Freeform, pinning
Language: English
Status: Completed
Published: 2017-10-02
Updated: 2017-10-02
Packaged: 2019-01-08 03:23:39
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 4,567
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/12246003
Author URL: https://archiveofourown.org/users/PurrfecktlySinful/pseuds/PurrfecktlySinful
Summary: Red and Sans have an argument. What could have gotten Sans so hot under the collar?A birthday gift for Soloshikigami, my good friend and fellow writer.Also tried a bit of a different technique for POV change in this one. I hope it works. :3





	A Heated Exchange

**Author's Note:**

  * For [SoloShikigami](https://archiveofourown.org/users/SoloShikigami/gifts).



1

“well what the FUCK was i supposed to do, Sans?” Red snapped, throwing his arms up in exasperation as he followed Sans into his room “the fucker was threatening you!”

“how’s about you let me handle it, Red?” Sans snapped back, turning to face him, his eye lights flashing with uncharacteristic anger. “i’m a grown god damned monster and can handle myself!”

“what’s wrong with me wanting to protect the monsters i care about? and what the hell’s crawled up your ass these past few days?” Red crossed his arms, glaring at Sans as though he wanted to punch him.

“what do you mean by that?”

“i mean you’ve been bitchy as hell!”

“i’m just sick of your hovering! you act like i’m made of glass or something!” 

Red snorted.

“you’ve got ONE fucking hp Sans!”

“GAH! So fucking what!?” Sans’ face contorted in a grimace of frustration “i managed to survive fine before we met! hell you even FUCK me like i’m gonna fall apart at any moment!”

Red choked and sputtered, his face turning a brilliant shade of crimson. 

“what the HELL, Sans!?”

“you heard me. you’re so worried about hurting me you don’t listen to what i want. it was cute at first but i wish you would grow a pair and fuck me into the mattress for once! at this rate my hand would be better!” 

Now Red’s face burned with anger as much as embarrassment. He ground his sharpened teeth and growled.

“i don’t have to listen to this bullshit.” he said, turning away from Sans.

“where are you going?” Sans asked

“Somewhere else, since it doesn’t matter if i’m here or not!” He snarled, stomping out of the room and slamming the door behind him.

 

2

“fine then!” Sans retorted “Fuck you and good riddance!” 

Stomping over to their bed, he picked up a pillow and threw it at the door. It fwumped against the wood and fell to the floor in a small poofy heap.

Swearing to himself under his breath, Sans stripped down to his boxers and cracked open the window. The argument had left him feeling hot and sweaty, and he wanted to get some cool air on his bones. Then he threw himself onto the bed and lay there staring at the ceiling.

He wouldn’t admit to listening for it but not long after that, he heard the sound of the front door slamming. Red really had left. 

Sighing unhappily, Sans absentmindedly scratched at a slight itch in his bones. They really didn’t have to argue about it. Red was just being concerned about him when one of the humans at the bar they had gone out to had decided to try stirring up some trouble with the two skeleton monsters. Sans was more than ready to play it off with a few well placed jokes and maybe offer to buy the guy a drink after warming him up a bit. It had worked before. However, before two words could be said Red had been there between them, eye lights glowing menacingly and a sharpened bone construct against the human’s neck. He had been radiating a magic and aggression that Sans had seen a few times before, and each time he had shivered at the display.

Why couldn’t Red show that confidence in the bedroom? It seemed like every time the spent time together Red was unsure and tediously gentle with Sans. It was infuriating. Sans had tried bringing it up with him before but Red had brushed it off so he had given up. He didn’t forget it though, and the dissatisfaction had settled deep in his soul, where it festered and grew. 

Until tonight.

Sans rubbed at his face, tears pricking at the corners of his eyes. He shouldn’t have said those things to Red. He really did just care about Sans, and in the world he came from protecting your mate was something that was both necessary and expected. However Sans HAD been feeling off the past few days. He had been short tempered and anxious, and so restless he could barely keep still.

And why the HELL was he still hot? He looked over at the window. He had definitely opened it earlier, and he could feel a light breeze playing across his bare ribs, but it barely had any effect on the warmth that seemed to stifle him.

Sans sat back up, fully intending to opening the window further. A sudden hot, tingling pleasure ran up and down his spine from the friction of the bed linens through his shorts. Something in Sans’ mind clicked and he looked across the room at the mirror set into his closet door. He noticed that he was WAY more flushed than any argument should have made him, his face and joints tinted blue with his magic. 

With a loud groan, he flopped backwards onto his bed, his arm flung over his eyes.

FUCK.

He was so screwed. 

 

3

Red stumped back up the front stairs to their home, swearing violently under his breath. 

When he had left, he couldn’t think of anywhere in particular to go, so he had taken himself over to his brother’s house. Edge lived with Papyrus, Sans’ brother, just a couple of blocks away in the same residential suburb of the city of Ebott. 

Edge had been surprised when Red had shown up alone on their porch, glowering at the ground with his hands shoved into his pockets. After staring at him for a few moments, Edge stepped back, opening the way into the house. 

“GET YOUR LAZY ASS IN HERE ALREADY.” He grunted, pointing inside the house with his thumb.

As they entered the kitchen, Edge motioned at the kitchen table.

“SIT.” He commanded. 

Out of instinct more than anything, Red sat. He continued to glare at the table in front of him with a stubborn, sulky expression as he listened to his brother clank around the kitchen. After a few minutes a plate appeared in front of him with a piece of chocolate cake on it. 

Red looked up in surprise and blinked at his brother. 

“what the hell, Boss. i thought you didn’t like sweets.” He said as Edge also set the usual cup of coffee in front of him. 

Edge coughed and looked the other way, a slight blush glowing on his cheekbones. 

“PAPYRUS MADE IT. HE DID NOT BELIEVE ME WHEN I SAID I DID NOT LIKE SWEETS. AFTER FINDING OUT I LIKED COFFEE HE SUGGESTED I TRY CHOCOLATE.”

“oh?” Red said, smiling smugly at his brother. Trust Papyrus to get his brother to try something new. Red always had to struggle to get Edge to try anything as a baby bones. “what did you think?”

“IT WAS… ACCEPTABLE.” Edge’s tone was gruff as he took his own piece of cake and sat down opposite Red. “NOW WHY ARE YOU HERE?”

Red was about to explain when there was a deafening clatter and slam from the front of the house. Red almost jumped up and summoned his magic, his nerves on edge. Who the hell would break into a house in the middle of the day!? 

Edge waved at him to sit back down, his expression calm, a small smile pulling at the corners of his teeth. 

“WELCOME HOME, PAPYRUS.” He called out

There were some further clunking noises not completely unlike a small herd of elephants and Papyrus came into the kitchen, his arms full of paper grocery bags. He peeked over the top of his parcels, only his wide eyes visible above the bags. 

“HELLO, EDGE! WOWIE, RED IS HERE TOO? DOES THAT MEAN MY LAZYBONES OF A BROTHER IS HERE TOO?” He chirped, contorting his neck every which way in hopes of catching sight of Sans. 

“NO. RED CAME ALONE.” Edge answered.

“OH.” Red could not miss the disappointment in Papyrus’ voice as he placed the groceries down on the counter. Then he turned and looked at Red with open curiosity for a few moments. “DID SOMETHING HAPPEN, RED?”

“HE WAS JUST ABOUT TO EXPLAIN WHEN YOU CAME IN”

So Red told them everything, about their date at the bar, Sans’ behavior the past few days and the incident with the other bar patron. 

“we were just heading out for some fresh air. sans said he felt warm and stuffy. then this fucker tried to pick a fight. i could tell Sans wasn’t feeling good so i stepped in and got the guy to back down.”

“WITH VIOLENCE NO DOUBT.” Papyrus said with a look of disapproval. Edge rolled his eye lights but let it pass. 

“well yeah, kinda. i mean, no one got hurt but i made it clear i wasn’t afraid to make my point… if you get what i mean.” Red said, forming a small, pointed bone construct above his hand. It hovered there a few moments before blinking back out. “anyways when we got home Sans just turns and… just starts bawlin’ me out! i was just trying to protect the guy. then he has to go and bring up our sex life and…” 

Red froze. Shit. he had gotten so caught up in his tirade he had forgotten who he was speaking to. He turned red, looking away. 

“OH PLEASE, RED.” Edge said, his voice dripping with sarcasm. “WE ARE HARDLY BABY BONES THAT YOU CAN’T TALK TO US ABOUT SEX. AND DESPITE HOW HE LOOKS,” Edge smirked and pointed at Papyrus, whose face had lit up in a bright orange color “NEITHER OF US WILL COMBUST IF YOU KEEP GOING.”

“E-EDGE!” Papyrus squawked, giving his boyfriend an offended look. Edge merely raised a brow back at him.

“well, uh… he just said i wasn’t aggressive enough…” Red mumbled, feeling mortified at having to talk about this to his brother and his brother’s alternate. he wondered if it was possible for him to shrink until he disappeared “said… uh… that i was afraid i’d hurt him and that his hand would be better.” 

“WELL THAT WAS HURTFUL AND UNCALLED FOR!” Papyrus said, his eyes widening in shock and sympathy.

“AND ARE YOU AFRAID YOU’LL HURT HIM?” Edge asked, his red eye lights piercing into Red.

There was a long, uncomfortable silence.

“maybe a little.” Red admitted.

Edge sighed. 

“SO IT HIT A BIT CLOSE TO HOME, AND YOU GOT MAD AND RAN OFF.” He summarized. Red winced, realizing that said like that, maybe his behavior had been less than mature. “WELL YOU DEFINITELY HAVEN’T CHANGED MUCH, BROTHER.”

“DID SANS EVER SAY ANYTHING ABOUT THIS TO YOU BEFORE?” Papyrus asked, his brow creased with concern.

“uh…” Red thought hard “he might have mentioned something before… maybe? i… don’t think i listened very well.” 

“HOW LONG AGO?” Papyrus pressed

“it’s been a while. i thought he had dropped it.”

This time it was Papyrus’ turn to sigh.

“OF COURSE. HE GAVE UP TRYING WHEN HE THOUGHT YOU WEREN’T LISTENING. HE ALWAYS GIVES UP TOO EASILY. ALSO I THINK HE HAS TROUBLE ASKING FOR HELP IN GENERAL. HE SPENT SO MUCH OF OUR CHILDHOOD MAKING SURE WE DIDN’T STARVE…” He said

Edge gave a snort of laughter.

“NYEH HEH HEH. I DO REMEMBER HAVING TO FORCE YOU TO LET ME TAKE OVER, BROTHER. YOU TWO REALLY AREN’T ALL THAT DIFFERENT.” He said

“IT SOUNDS LIKE YOU TWO NEED TO HAVE A GOOD TALK. I… AM A BIT CONCERNED THOUGH. SANS USUALLY ISN’T SO… VOLATILE.” Papyrus looked thoughtful “RED, DID YOU SAY THAT SANS HAS BEEN TEMPERAMENTAL FOR THE PAST FEW DAYS?”

“yeah. he’s been really pissy.” Red grumbled.

“AND YOU SAID HE WAS FEELING WARM AT THE BAR?”

“that’s what he said.”

“DID HE SEEM FLUSHED?”

“ummm… i guess? we were both yelling. he was really sweaty though. why? is he sick?”

“MAY I SPEAK TO YOU A MOMENT, EDGE?” Papyrus said, tugging at Edge’s shoulder.

Red gave them a puzzled look as they stepped out of the room. He heard them talking, Edge’s voice low and raspy, Papyrus’ voice rapid and excited. For once, both of them were watching their volume, so he couldn’t hear any details, until…

“NYEH HEH HEH! THAT’S FUCKING HILARIOUS!” Edge bellowed with laughter.

“HUSH! AND WATCH YOUR LANGUAGE, IT’S NOT FUNNY!” Papyrus cautioned.

“WELL IT CERTAINLY FIXES THINGS, DOESN’T IT? I KNOW JUST WHAT TO DO.”

Red heard the confident steps of his brother as he stomped his way back to the kitchen and then straight towards him.

“hey, Boss, what’s uuUUUUUPP—WHAT THE FUCK!?”

Sans yelped as Edge grabbed the back ruff of his jacket, hauling him up into the air. Red’s legs kicked at space as his brother marched with him in tow to the front door. With one efficient motion, Edge tossed red outside, where he landed on the front step with a WHUFF, bruising his tailbone.

“BROTHER, YOU NEED TO GO HOME AND FIX THINGS UP WITH SANS RIGHT NOW. AND DON’T YOU FUCKING DARE SHOW YOUR FACE AROUND HERE TILL YOU DO, AM I CLEAR?” Edge barked, adopting the tone he used to use with the dog brigade back in Snowdin. Then the door slammed shut, leaving Red no room whatsoever to argue.

And so Red had stomped his way home, uttering blasphemies and epithets the entire way.

He paused with his hand on the doorknob and took a deep breath. It couldn’t be that hard, right? Just go in, apologise and have a nice talk to sort things out. He just had to swallow his own damned pride and get Sans to stop being a stubborn jackass long enough to listen.

Red chuckled.

“yeah, not hard at all for two boneheads like us.” he said to himself, his voice dripping with sarcasm.

The smell hit him like a truck the moment he walked in. Sweet and spicy, the musk filled his nasal cavity, making him feel dazed and intoxicated. There was a low buzz of excited magic in the air and his own responded eagerly, singing through his bones and making his soul ache. 

“fuuuuuck” he muttered, swaying slightly on his feet from the heady scent surrounding him. Well that certainly explained Sans’ recent moodiness… and their brothers’ reaction earlier.

Sans was in heat.

Red thought about Edge’s command to ‘fix things up’ with Sans. That fucker was probably having one hell of a laugh at their expense right now and he reminded himself to kick his brother’s ass later.

How the hell were they going to have a talk like this?

He kicked off his shoes and removed his coat. He was beginning to feel too warm, even though they kept the house at a cool temperature. After all, they were skeletons and didn’t need much in the way of heating under normal circumstances. With single minded purpose he strode up the stairs to the door of Sans’ room. 

He stopped there, uncertain about whether he should just go in. Sans’ heat-scent was so strong Red was having a hard time thinking straight. Should he knock? Would Sans even want him to help? He had said earlier that his hand would be better. Red felt positive that had been the anger speaking but could he really be sure?

His soul wavered. Maybe he should just leave and let Sans cope with his heat on his own. If Sans wanted help he would come and ask…

Right?

A loud clatter, followed by a thump and a sharp yell halted further thought. Alarmed, Red pushed his way into the room, his soul thumping in his chest. 

Sans lay in the middle of his bedroom floor, turned away, curled in on himself and groaning. The blanket had been dragged off of the bed in a long trail, ending in a loop of fabric caught on his foot. Obviously it had been what had tripped him as he was getting out of bed. Since Red had left he had stripped down to nothing but his shorts, and even those were hitched down around his thighs, exposing his pelvis and the bright glow of blue magic there. 

Red rushed to Sans’ side, his own arousal forgotten for the moment, drowned out by concern that Sans might have hurt himself.

“Sans! oh stars, are you okay?”

 

4

Everything burned.

He was so hot. Sweat slicked his bones and his magic throbbed with a deep aching need. Touching himself brought only mild, temporary relief, and the effects of his heat were starting to border on the painful. He needed help… He needed Red.

He had just barely heard the slam of the front door, followed by the sound of footsteps coming up the stairs toward his room. It was Red… he must be home!

Desperate to get to him, to let him know how much he needed him right now, Sans sat up and crawled to the edge of the bed. Somewhere along the way his feet got tangled in the sheets, and in his effort to dislodge them he fell off the bed and tumbled, ass over tail bone onto the carpet.

He groaned pathetically, tears stinging his eyes. It wasn’t like Red would want to help him anyways. He had been nothing but a bitch for the last few days and it had probably driven his edgier self to hate him. After all, who would want to put up with a pathetic excuse for a skeleton like him.

He curled in on himself, willing the misery and discomfort of his heat to go away. His hand traveled down to the sensitive slit his magic had formed, brushing lightly across the slippery outer folds. He shuddered as a fresh wave of warm tingling radiated from his pelvis.

A hand fell on his shoulder and shook him, and that was when he realized that someone had been calling him. 

“Sans, Sans are you okay?” 

Red… it was Red.

Red gripped his shoulder gently and pulled him over onto his back. Sans stared back at him in bewilderment.

“Red?” he rasped

“heh, yeah, it’s me.” Red answered, the relief showing clearly in his crimson eye lights. Then he looked Sans up and down, his expression changing to one of barely concealed hunger. “you , uh, okay there, bud?”

Sans grabbed the front of Red’s t-shirt, tugging at it pleadingly.

“please, Red… i need you… please…” he begged, a whine edging his voice.

Red seemed to make an almost physical effort to restrain himself. Sans could feel his mate’s magic responding to his own, a red glow shining below the fabric of Red’s pants. It felt so good just being this close, just having the warmth of his presence next to him, but he needed more. Why wasn’t Red giving him more?

“Sans, we need to talk…” Red started.

Anger and frustration flared in Sans’ soul. Why the fuck was he still talking? God damn it why wouldn’t Red give him what he needed?

With a burst of strength Sans wrapped the fabric of Red’s shirt around his hand and yanked hard, jerking him forward so they were face to face. 

“will you quit dicking around and use that limp noodle between your legs for what it’s meant for!? fuck me already!” He snarled, baring his teeth so that his dull fangs showed in the dim light. 

Something flashed in Red’s eyes, something wild and primal that made Sans shiver, feeling a flash of fear and anticipation that only made his magic race faster through his bones. Then Red was pushing him down, pressing against him hard, his tongue invading Sans’ mouth with a greed he had never felt before. He willingly submitted, allowing Red to dominate him, his own tongue being pushed back as Red’s curled around it, hot, slick and prickling with energy. 

Muffled by their kiss, Sans gave a choked cry as two of Red’s fingers forced their way into him, rough and insistent, stretching him with a sweet, aching pleasure that had his hips bucking into them, forcing them deeper. His passage clenched and fluttered around the intrusion as his soul quivered, slowly beginning to leak liquid magic onto his spine in small, warm drips that dribbled between the cartilage in tickling blue lines. 

Red pulled away from the kiss, and another finger joined the other two before Sans was quite ready for it, making him whimper, tears dripping down his cheeks at the intensity of the sensation. He caught a faint, hazy glimpse of Red licking his teeth with a predatory grin before he was on Sans again, his teeth latching hard onto the sensitive bones of Sans’ neck. 

“AAAHHH!” Sans yelped, the pain immediate and intense, blending with and intensifying his pleasure in a way that made his spine arch. He came, his whole body quaking, a gush of fluid wetting his femurs and no doubt Red’s hand. He collapsed limply onto the carpet, panting and shaking. A trickle of something warm ran down his neck, which Red lapped up with a pleased rumble in his throat. The wet warmth of Red’s tongue and the sting as it ran across the bite felt good, and Sans gasped, his head spinning with relief now that his heat was partly sated.

“i hope you don’t think i’m finished with you yet.”

The words sent a chill down Sans’ spine as Red grabbed him and flipped him over. Before Sans could collect himself his ass was in the air, Red’s hand pressing down on the back of his neck, pinning him to the floor. Grunting, he squirmed against the pressure on his cervical vertebrae, but Red was hellishly strong when he wanted to be and Sans found he wasn’t going anywhere. He heard the rustle of fabric and Sans felt the heated nudge of something against his entrance. 

It was the only warning he got. 

Snapping his hips forward, Red buried his cock deep in Sans’ dripping magic. Sans keened, the pressure of being suddenly filled setting his heat on fire all over again. It was almost too much, and his hands scrabbled against the coarse carpeting of the floor. 

“ffff…aaahh… Red… so biig… nnnggh…” He wriggled, unsure whether he wanted to push back or pull away. His soul throbbed in his chest and his magic prickled and tingled with ecstasy. It was so fucking good, but it was also so fucking much!

Red didn’t bother giving Sans time to adjust, immediately pulling out and driving back into his counterpart over and over, rutting into Sans relentlessly, driven wild by his partner’s heat-scent. Sans Sobbed and moaned with each thrust, feeling himself being pressed down by the weight of Red’s body over him and the sharpened fingertips digging painfully into his neck. He could feel the carpet dragging roughly across his cheekbone with each sharp movement, a burning friction that only seemed to enhance the raw animal pleasure coursing through his bones. Red was dominating and claiming him completely, and Sans felt the fear and thrill of the experience push him into a dazed euphoria where he couldn’t even think anymore.

“god, Sans… so tight… so fucking good…” He barely heard Red gasping above him, overwhelmed by the fire in his body, his walls fluttering and pulsing around the thick member drilling into him.

Sans didn’t know how long it lasted, but at last Red’s hips stuttered and he let out a gutteral, halting moan as he buried himself in Sans one last time, spilling into him as he finally reached his peak. The hot magic that filled him pushed Sans over the edge a second time, and he screamed and arched as his passage clenched around Red’s cock, milking it dry. Then Sans went limp and passed out.

 

5

Red didn’t think he’d ever felt happier than when Sans opened his eyes.

After he had come down from the high of his orgasm, Red’s senses had returned to him and he found himself slumped against Sans’ motionless form. To say he had panicked had been an understatement. He called out to Sans frantically, shaking his shoulder, his soul racing as cold fear clawed at it from within. Sans hadn’t responded at first, and Red was about to dive for his cell phone and call his brother when he thought to check Sans’ stats.

Okay… Stats were okay, HP was okay… Sans had just passed out.

As if that weren’t bad enough.

It had taken him some time, but somehow he had managed to get the sheets on the bed changed and Sans cleaned up before tucking him into the clean comforter. After that he had pulled up a chair and refused to leave his partner’s side, holding one of his hands in both of his own. 

Red was beginning to drift off when a soft groan snapped him awake. Sans shifted, turning his head and opening his eyes, disoriented and groggy.

“fuck. what hit me?” he asked.

“one heat cycle and about 100 or so pounds of lust crazed skeleton.” Red said sheepishly

“ah… that explains the aching pelvis.” 

“oh fuck, Sans. i am so sorry. i shouldn’t have…” Red began to babble

“shut up, Red. you didn’t do anything i didn’t want done to me.” Sans stretched a bit, winced, and then decided it might be better to remain still for the time being “i haven’t been fucked like that since… well, it’s been a while.”

“ugghh… i can’t believe i lost control like that.” Red groaned.

“i was… AM… in heat, Red. you know a heat affects anyone in distance of the smell. you couldn’t help what happened. i’m actually glad’ Sans chuckled and gave Red a sly smile “I need to bottle me some of that for future use.”

Red snorted with laughter.

“and people think I’M the pervert in the relationship.” he said

“still waters run deep.” Sans replied, shrugging and winking at him.

“listen, Sans, i’m sorry i yelled. And you’ve tried to talk to me about… things before and i think i might have brushed you off…”

“nah” Sans waved him off “don’t worry yourself about it. i was being a real ass these past few days and was way out of line.”

“no, Sans.” Red insisted, squeezing Sans hand and looking at him seriously. “you’re important to me. we need to talk about this. i want us both to be happy.”

Sans stared at him for a long time, and Red’s soul flip flopped in his chest as he waited to hear Sans’ response. Would he take him seriously? He wouldn’t blame Sans for brushing him off the same way he had brushed Sans off before…

“sure, Red.” Sans finally said, smiling fondly at him “you’re right, we should talk.”

“good.” Red affirmed

“however.” Sans yawned, scooting toward the other side of the bed and lifting the blanket in invitation. “i’m still in heat, and while you’ve fucked me senseless once already, it’s only a matter of time before it surges again. i’d like to get some sleep before that happens. join me now and wreck me again later?”

Red chuckled, shaking his head at Sans’ saucy behavior.

“sure thing, babydoll.” He said, climbing into the bed and arranging the blankets around the both of them. He sighed in contentment as he snuggled in close to his lover.

Sleep came quickly and claimed them both, their arms wrapped around each other in comfort and love.


End file.
